Peroxide-Selective Reduction of O₂ at Redox-Inactive Rare-Earth(III) Triflates Generates an Ambiphilic Peroxide

Area of Science:

• Inorganic Chemistry
• Organometallic Chemistry
• Catalysis

Background:

• Metal peroxides are crucial in biological and synthetic processes.
• Rare-earth peroxides are implicated in catalysis but have been poorly studied.
• Limited reactivity studies exist for isolated, characterized rare-earth peroxides.

Purpose of the Study:

• To report the selective reduction of dioxygen to peroxide using rare-earth triflates.
• To isolate and characterize the first molecular praseodymium peroxide.
• To investigate the reactivity and mechanistic pathways of rare-earth peroxides.

Main Methods:

• Peroxide-selective reduction of dioxygen using decamethylferrocene (Fc*) and rare-earth triflates in methanol.
• Isolation and characterization of praseodymium peroxide (2-Pr) via single-crystal X-ray diffraction, Raman, and NMR spectroscopy.
• Protonation studies and reactivity assessments (electrophilic and nucleophilic).

Main Results:

• Achieved high peroxide selectivity (93-99% O2^2-) in dioxygen reduction.
• Successfully isolated and characterized the first molecular praseodymium peroxide, [PrIII2(O2^2-)(18C6)2(EG)2][OTf]4 (2-Pr).
• Demonstrated high thermal stability of 2-Pr and its reactivity in oxygen atom transfer and phosphate-ester cleavage.

Conclusions:

• The rate of oxygen reduction is governed by metal-ion accessibility, not Lewis acidity.
• Weak metal-ligand interactions preceding electron transfer can enable differentiated reactivity of redox-inactive metal ions.
• Opens new avenues for catalysis and synthesis utilizing rare-earth metal centers.